A wireless communication network generally consists of various transceivers (transmitters and receivers) that achieve inter-communication by means of the emission of electromagnetic waves. These transceivers, which are also referred to as radio access equipment, exist in different physical sizes and have different transmission/reception capabilities that are characterized by factors such as maximum signal transmission power levels, information transmission bit rate capability, ability to transmit or receive signals to/from a number of other transceivers, and supported frequency bands of operation. In terms of current systems, examples of this type of radio access equipment consists of small portable terminals such as cellular phones with multiple band capability or personal digital assistants with wireless access capability, portable radios with multi-band capability and higher power than cellular terminals, cellular base stations, wireless LAN access points, wireless cards installed in portable computers, etc.
Such radio access equipment can be classified into two categories: i) equipment that is shared by multiple users, i.e. undertakes communication to multiple users in different locations, and ii) equipment that is dedicated to a particular user. Shared equipment forms part of what is generally referred to as the network infrastructure. This equipment, or infrastructure, is deployed throughout a geographical service area. Other transceivers that venture into this area can communicate with the infrastructure equipment in a manner that is known.
Wireless networks can be classified in terms of the types of transceivers that they incorporate. These networks can be classified as i) infrastructure-only, ii) infrastructure-terminal, and iii) terminal-only. Microwave point-to-point networks are examples of i) since there are no terminals, cellular networks are examples of ii) since they include base stations and terminals, and ad-hoc networks such as WiFi (IEEE 802.11b & 802.11a) operated in ad-hoc mode are examples of iii).
Considering networks with infrastructure, in the most common case individual infrastructure elements are placed in fixed locations and connected to a fixed wire-line network such as a public switched telephone network (PSTN), a cable TV network (CATV), a power-line communication network, or to a local area network (e.g. Ethernet) that is connected to the Internet. An example is the case of cellular networks where the wireless transceiver that forms part of the infrastructure is called a radio base-station. In the case of local area networks current examples are access points for wireless LANs. These access points form gateways from a wireless LAN to a fixed network.
The first category of equipment in the above (shared by multiple users) is typically referred to as network equipment, and the second category is called terminal equipment. The network equipment is however not required to be fixed, and it is possible that future networks may have mobile base stations. In fact one example of such mobile base stations is base stations that are installed in moving platforms such as trains, buses, ships, and airplanes. One characteristic of network equipment versus terminal equipment is that typically it has a higher cost, is physically bigger, and typically has the capability to provide a connection to a number of terminals simultaneously.
The nature of current network infrastructure is that it must be deployed (or installed) using a non-trivial procedure, and often by a specialist, in order for a network to exist. We may classify the resulting networks into two categories, those that are installed and meant for the use of a private company, institution, (or household), where the set of users is restricted to a specific group, and those that are meant for the use of any member of the general public who undertakes a service contract with the so-called network operating company. Networks of the former type are called private networks, whereas networks of the second type are called public networks.
Currently cellular networks are the prime examples of wireless public networks, whereas local area networks, such as WiFi, set up in private companies or homes, are prime examples of private networks in the sense that they are meant to interconnect with a limited specific set of terminals. WiFi networks set-up to provide the so-called hot-spot service are examples of public networks. The main difference between cellular networks and hot-spot networks based on WiFi is that in the case of cellular networks, the network has a very wide coverage, and in many cases it covers whole countries. Hot-spot networks on the other hand cover specific limited locations and in some cases a number of these locations are interconnected by the same fixed network and managed by a single network operating company to form a single network with non-contiguous coverage.
As mentioned above, networks can be categorized into those that have an infrastructure component and those that are purely ad-hoc networks (terminal-only). The design of wireless networks with infrastructure components and mobile terminals has its roots in telephony, where the goal is to provide telephone service anywhere in a large coverage area and in effect introduce mobility to telephone networks. On the other hand, the design of purely ad-hoc networks has its roots in military communications that itself gave rise to the Internet. The design of communication networks is typically carried out using an approach that divides the overall task into a set of tasks that address issues at different levels of abstraction. There is a well known OSI 7-layer reference model that is used. In the case of wireless networks the physical layer refers to the level of abstraction, in this model, that addresses issues of modulation, error control coding, multiple access, and many other issues including power control and hand-offs.
Currently there are two main classes of wireless networks that are widely used: i) the cellular networks that are based on the various physical layer designs such as AMPS, IS-136, PDC, GSM, IS-95 (CDMA or “Code Division Multiple Access”), CDMA2000, and WCDMA, TD-SCDMA, and ii) the wireless LANs that are based on the physical layers IEEE802.11b,a,g. The different cellular standards have been classified into generations and currently we are at the third generation. As a result we will refer to all these cellular network technologies as 3G—since this is the current status of this line of technologies. In the case of wireless LANs the main physical layer currently in use is IEEE802.11b and IEEE802.11a and is referred to as WiFi.
The physical layers for 3G and WiFi are significantly different. The main reason for this difference is that the design of the WiFi physical layer was based mostly on the purely ad-hoc networking concept, whereas the design of 3G and all its predecessors was based on a network with infrastructure where a set of somewhat regularly placed base-stations provide coverage over a wide geographical area. However, as a result of wireless industry circumstances, the success of the 3G system in providing Internet access has been less than expected. On the other hand, the wireless Internet access based on the WiFi air interface has been successful not in the purely ad-hoc mode but in the infrastructure mode, i.e. in a mode where all access point that is attached to the Internet is employed. In a sense we have the WiFi network succeeding in an area for which the 3G air interface was designed, i.e. as an infrastructure network to access the Internet albeit with limited coverage.
In spite of the different design criteria, both the 3G and WiFi technologies are generally being used mostly as infrastructure for access by terminals. For the sake of clarity, “terminal” in this disclosure generally refers to a network-connected device associated with a user including a cell phone, handheld device, personal computer, or other computerized devices capable of wireless network connectivity. The key difference between these two technologies is the manner in which they are being deployed. The nature of deployment of a wireless network infrastructure is an important issue. In the past we have had a tremendous degree of emphasis on the capacity per unit base station as the key issue for the design of different air interface technologies. This capacity can typically be measured in terms of the number of voice users that a base station can support per MHz of spectrum allocated, or the aggregate bit rate per base station per MHz of spectrum in supporting a number of terminals. A huge degree of development in the different generations of cellular systems has been guided by this basic principle of maximizing the spectral efficiency per base station. These base stations are typically costly to install. This is because they are usually meant to cover a large service area and require a comparatively large power amplifier that is generally expensive. In addition, the installation of the transmitting antennas generally requires the rental of private facilities at the top of private buildings. Also, selection of a site to install a base station generally requires a very careful study of signal propagation and signal coverage by RF network planning engineers. These engineers represent perhaps the group of employees of an operating company with the most specialized sets of skills that are in many cases acquired in graduate university programs. Accordingly, they are generally a costly resource. The installation also entails the selection of transmitter power levels and antenna orientation. In a CDMA system such as IS-95 (2G) or CDMA2000 (3G) the installation also requires the configuration of the software with many parameters such as the initialization of the pilot offset neighbour lists, pilot search windows, pilot thresholds for the hand-off algorithm, etc. In a GSM (Global System for Mobile) network the configuration entails the selection of broadcast channel parameters, power levels, set of RF channels for transmission, and the frequency hopping algorithm to decide on the sequence of RF channels selected for transmission.
As mentioned earlier, the wireless cellular industry is now deploying third generation cellular systems—the so-called 3G systems. Third generation systems in the North American context exist in two possible modes—the so-called 1X and 3X modes. We are seeing the deployment of the 1X version, and it is not clear that there will be a business case for the deployment of the 3X version. The 1X system is based on a 1.25 MHz channel bandwidth that is compatible with IS-95, whereas the 3X system is based on the use of CDMA RF carriers with 5 MHz channels. In the forward link the multi-carrier option is used, whereas in the reverse link a direct spreading scheme with 3 times the IS-95 chip rate is used. The 1X system has a lower limit maximum bit rate that a user can achieve, however this is similar to the data rate goals of 3G in general. Also new developments in the 1X system, such as terminal antenna diversity, can improve the data rate. The result is that there may not be a compelling technical reason to introduce the 3X version.
The other main 3G standard is the European standard that is being positioned as the evolution of the GSM system in the direction of CDMA technology. Like the CDMA2000 3X system, the system utilizes RF CDMA carriers that occupy 5 MHz bands, but has quite a few differences in comparison to the CDMA2000 standard.
Meanwhile we have a major research program throughout the world targeting the next generation of wireless cellular systems. This generation is generally referred to as 4G, or beyond 3G. There is no general consensus as to what are the goals for this system except that somehow it should have more capability than the 3G systems to provide future services.
There is some expectation, however, that the progression from 3G to 4G (whatever it turns out to be) will be very different from the progression for the various generations up to 3G. The evolution of the different generations up to 3G basically stressed higher bit rates and greater network capacity for a given amount of allocated spectrum. For most of these systems the concept of the system remained somewhat the same. We had a series of more or less regular cells covering a service area with the base stations placed at the centers of cells. There were variations in cell size in the sense that we had macro-cells, regular-cells, micro-cells, even pico-cells. However the deployment strategies for these systems, remained somewhat constant. A cellular operating company acquired radio spectrum, with the price becoming increasingly higher over the years. It bought infrastructure equipment, installed this equipment using its specialized engineering capability and provided services to the public. Usually the services were billed by time, with some flat rate portions of plans at off-peal hours, or in the case of data services the billing could be per Mbyte of data transferred.
A major characteristic of the current status of the cellular system industry is the very high valuations placed on the radio spectrum as evidenced by the price that certain modest blocks of spectrum attained in spectrum auctions, especially in Europe where the values reached into the range of billions of dollars. As a result of these auctions many of the cellular operators were left without capital for investment in the 3G infrastructure, the introduction of higher data rate services was delayed, and the result was that the manufacturing sector was left without demand (or lesser demand) for the 3G technology that it had created.
At the same time wireless LAN's have become quite successful in the market place. These LAN's are based on the IEEE 802.11b and IEEE802.11a standards and utilize the ISM bands at 2.4 and 5 GHz. However these LAN's were designed with the emphasis on communication between terminals in an ad-hoc manner. As mentioned above, the channel access protocol used comes from the older research in packet radio network protocols that was developed with military applications in mind and meant for use in an environment where a number of terminals come together in an ad-hoc manner. However the current reality is that these networks are being used mostly in an infrastructure mode where they communicate with a base (the access point) that is connected to the Internet. A very successful use of this technology is in home area networks where the access point is incorporated into a router that interfaces a local area network in the home to a modem that connects to the Internet either through DS, cable TV system, or a power line based local access system. The access point now sells for the price of a terminal.
As a result of the design, with emphasis on ad-hoc operation, IEEE 802.11b networks are not very efficient in terms of spectrum usage, especially if they are being used in an infrastructure mode, so it is not clear what will happen with the resulting interference when a large number of access points are deployed in close proximity. It is likely that significant degradation of quality of service will occur. Also, there will be stress put on the system once wireless applications start requesting greater channel bandwidth than those currently available. Also, this is a technology that is different from cellular technology, although it is possible to build equipment that would automatically allow inter-operation of these two networks in a seamless manner. Whether these shortcomings are sufficient to stop the advancement of WiFi technology as it encroaches more and more into the cellular systems is not clear.
It is clear from the above that what is required is a type of network that has some of the characteristics of today's ad-hoc networks (based on the successful WiFi technology) in terms of ease of deployment and at the same time the characteristics of cellular networks with wider area coverage and higher spectral efficiency.
What is needed therefore is a communication network, system architecture and method of network deployment that allows expansion or deployment of the network by relatively easy installation of network infrastructure components, so as to allow network growth in an organic fashion in response to ad-hoc demand for capacity What is also needed is a method of deployment of a network that can be customer driven (users or private enterprises) or by the network operating company in a manner that is relatively fast and low cost.